The time consuming and complex part of painting lies in the detail work. Such work includes corners, trim, molding, windows, utility connections, and so forth. When confronted with such numerous items to paint around, a novice will reach for painter's tape. But applying tape to every surface adjacent to the area to be painted is time-consuming and wasteful.
Thus, a painter may wish to “cut in” the room first. Cutting in is the process of painting around the joints of the wall and the edges where the wall meets the ceiling or the moldings. A novice, lacking the steady hand of a professional, has to choose between two types of imperfect brushes. He can use an angled sash brush/peacock brush, but given the lack of fine control he is likely to accidently apply paint to adjoining surfaces. Or he can use a trim angle sash brush/rattail brush, but its small size results in many trips back to the paint bucket, negating the time benefit of skipping the tape.
What is needed is a paintbrush that provides the fine control and forgiveness of a small brush, but the paint-carrying capacity of a large brush.